Wi-Fi Protected Access (WPA) and Wi-Fi Protected Access 2 (WPA2) are wireless security protocols proposed in the IEEE 802.11i specification. For enterprise network environments, WPA/WPA2 requires authentication in two phases. The first is an open system authentication and the second uses IEEE 802.1X with an Extensible Authentication Protocol (EAP) authentication method. For environments without a Remote Authentication Dial-In User Service (RADIUS) infrastructure (e.g., small office/home office networks), WPA/WPA2 Personal supports the use of a preshared key (PSK).
WPA/WPA2 requires the determination of a pairwise master key (PMK) based on the EAP or the PSK. WPA/WPA2 also requires the calculation of pairwise transient keys (PTKs) through a 4-way handshake.
In particular, WPA-PSK (Wi-Fi Protected Access with Pre-Shared Key) and WPA2-PSK (Wi-Fi Protected Access 2 with Pre-Shared Key) are commonly implemented and used in today's wireless networks for security purposes. WPA-PSK/WPA2-PSK uses a key generation function to calculate a pairwise master key (PMK) based on a static passphrase. The PMK remains unchanged in subsequent associations unless the static passphrase is changed on a client system and an access point. Thus, in general, clients and access points use a same PMK in the WPA-PSK/WPA2-PSK mechanisms unless the static passphrase is changed.
In other words, if a PMK of a client is compromised, network security of all other clients connecting to access points in a same network is also compromised. Additionally, with advances in high speed computing, it is now possible to determine a correct passphrase from millions of combinations, in a reasonably short time frame, by performing brute force attacks.